Discontinuous, asymmetric and irregular colour patterns in Silurian oncocerids (Nautiloidea) with cyrtoconic shells

Abstract

no­ typic characters in ectocochleate cephalopods. The origin and biological function of colour patterns is a matter of ongoing discussions and well­founded data concerning its evolution are still very limited (Williams 2017). However, the poor knowledge on colour patterns in fossil ectocochleate cephalopods significantly increased in the last decades (Mapes & Davis 1996, Turek & Manda 2011, Mapes & Larson 2016). Colour patterning of the nautiloid shell was studied in relation to animal phenotype, autecology, habitat and taphonomy; the applicability for nautiloid taxonomy was discussed (Ruedemann 1921, Foerste 1930a, Kobluk & Mapes 1989, Mapes & Davis 1996, Manda & Turek 2009a). Up to now, colour patterns are documented in 47 early Palaeozoic nautiloid species (for a list with references, see Tab. 1). We have not regarded those species, in which colour patterns were mentioned (Foerste 1930a, Strids ­ berg 1985) but neither illustrated nor described in detail (see Turek 2009). Colour patterns in Early Palaeozoic nautiloids have been recorded in representatives of the orders Oncocerida, Discosorida, (both subclass Multiceratia), Tarphycerida and Nautilida, while colour patterning in evolutionary older Cambrian and Early Ordovician nautiloids is still unknown. The vast majority of species displaying colour patterns belong to the order Oncocerida possessing straight or slightly curved breviconic shells (Barrande 1865–1870, Foerste 1930a). Colour patterns in oncocerids with coiled or almost straight shell were documented in only a few cases (Manda & Turek 2009a, Turek 2009). Oncocerids display a high disparity of their shell form, ranging from straight, slowly expanding to coiled, trochoceraconic forms (Sweet 1964, Dzik 1984, Manda & Turek 2009b), which is linked to the disparity in colour patterns. The colour patterning in Multiceratia includes longitudinal and